In the manufacture of corrugated boxes, the preslit box board is commonly glued and folded into a flat tubular shape in a folder-gluer machine. In such machines the boards are carried on a conveyor through a gluing station at speeds in the range from a few hundred feet per minute to well over one thousand feet per minute. The glue is applied to the manufacturer's flap or tab, or to the portion of the board to be glued thereto, in a narrow band or stripe by means for example, of a pneumatically operated spray head. Following the gluing operation each board is folded into a flat tubular shape and the glued surface is pressed against the opposing surface. Operation of the spray head or other glue applicator is controlled by means of digital pulses which are generated for each predetermined increment of movement of the conveyor, and these pulses are counted to trigger the controls which cause a valve in the applicator to open and close. These pulses are also used to control the volume of glue which is sprayed from the head to insure a uniform glue density in the pattern irrespective of changes in the conveyor speed.
There is a constant time lag between the occurrence of each trigger pulse which initiates the spray and the time when the glue actually reaches the surface of the board. This time lag includes the time required for the valve in the spray head to operate and the time required for the liquid to travel from the head to the surface of the board. There is another time lag between the occurrence of each trigger pulse which terminates the spray and the time when the application of glue to the board actually stops. Since the amount of board movement during these two fixed time lag periods is related to the conveyor speed, in the prior art glue applicators the longitudinal position of the glue band or stripe has varied when the conveyor speed varied. This variation in glue stripe location presents several problems including, for example, overspray at the front and rear ends of the boxes. Of course, where the system is used for those applications where the pattern must be precisely located, variations in pattern location cannot be tolerated.